The speaker
The speaker of "Wife" is a woman who is married and is pondering her discomfort with word "wife." She feels some distance between herself and the "single girls" in her life—unmarried women who may be friends or acquaintances and are probably younger than she is. Contrary to the ingrained social expectations of a wife who is productive, obedient, and never sad, the speaker is often paralyzed by melancholy and grief and can spend long mornings doing nothing but staring out the window. She feels a strong disconnect between her reality and the assumptions of what a "wife" is. She loves her husband, or wants to, but worries that she isn't "good" at loving him, and wants to make sure that her love for him doesn't mean that she becomes anything less than what she is.
The single girls
Younger friends of the speaker who appear in lines 3-7. At dinner, they roll their eyes in judgment about a friend who is going on a trip that has not been approved by his wife. They seem ridiculing or derisive of marriage, since they are unmarried. In return, the speaker seems to feel the distance between herself and the single girls, describing their "pretty young heads" with an ambiguous mix of admiration and condescension.
the famous feminist
The poem includes an italicized quotation from a satirical 1971 essay by Judy Brady, who is only referred to as "the famous / feminist." The quote is an example of the impossible sexist standards that wives face, which the speaker relates to.
the husband
The speaker's husband is only referred to late in the poem, twice, by the second-person "you" in lines 21 and 24. The speaker loves him and wants to be his, and doesn't want this fact to turn her into some lesser kind of person.